Connections between the commutator segments and the armature coil wire have been made using a hot forging process. A tang is provided on the commutator segment and is bent over to enclose or trap the wire. An electrode is brought down onto the tang to bend it over against the commutator segment, trapping the wire in between. Another electrode bears on the segment and a current is passed between the electrodes to heat the tang, the pressure and heat serving to forge a free end of the tang onto the segment to form a sticking contact between the tang end and the segment. Insulating resin coating on the wire is burnt off during the hot forging process so that there is electrical contact between the wire and the commutator segment and tang. In fractional horsepower motors of this type it is important that the electrical resistance of the motor, and hence of any electrical connections in the motor, be kept to a minimum. When using the hot forging process with large diameter wires it is found that, in use, the resistance of the wire-segment connection may increase to an unacceptable level. Although the large diameter wire is trapped by the tang, it tends to flex and move due to the centrifugal forces on it and differential expansion as the motor heats up and cools down, resulting in a loose mechanical connection and hence a poor electrical connection.
It is known to pre-tin the segments of the commutator before hot forging. The reasons for doing this are not clear but it does not result in a significant improvement in connections with large diameter wires and it is necessary to remove the tinning from brush contacting surface of the segments before the commutator is used.